1. Field of the Invention
The present invention relates to the releasing of a molded ophthalmic lens from a mold surface and in particular to the dry release of a lens formed of a compliant material from a mold.
2. Description of Related Art
The molding of contact lenses is known in the art and reference in this regard is made to U.S. Pat. No. 5,466,147 the disclosure of which is incorporated by reference. Briefly stated, a contact lens generally is formed in a single use mold unit comprising a female mold section having a concave optical surface and a male mold section having a convex optical surface. The male and female mold sections are formed of a single use deformable material and are complementary shaped. The mold sections are brought together to form a lens-molding cavity between the facing convex and concave mold surfaces.
To form the lens, a quantity of lens forming material first is dispensed into the concave optical surface of the female mold section. In the context of the present invention the lens forming material is a mixture for producing a silicone-containing hydrogel lens. An appropriate mixture for making a silicone hydrogel lens is known in the art and reference is made to U.S. Pat. No. 5,260,000 the disclosure of which is incorporated herein by reference for a description of the process.
Briefly, and as disclosed in U.S. Pat. No. 5,260,000, the process involves preparing a monomeric mixture comprising a silicone-containing monomer, a hydrophilic monomer and an organic diluent. This mixture is charged into the mold and then the male mold section is seated upon the female mold section such that a lens forming mold cavity is formed therebetween. The joined male and female mold sections form a single mold unit that under goes a curing cycle to polymerize the lens material in the mold cavity. Once the lens material is cured, the mold sections are separated to retrieve the cured lens.
Upon mold separation the cured lens generally adheres to the concave optical surface of the female mold section. The problem then is to effect the release of the cured lens from the female mold section without damaging the lens. In most cases a dry release of the cured lens can be accomplished by a method as disclosed US Publication No. 2004/0061246.
In this respect the method as disclosed in US Publication No. 2004/0061246 uses a plunger that that has an annular ridge on an end surface. This annular ridge has a flat end face, which is pressed against the anterior surface of the female mold section. Since the anterior surface of the female mold section is curved (convex) the flat end face of the raised ridge has a relatively sharp edge that first contacts the curved anterior surface of the female mold section. The force exerted by the plunger against the anterior surface of the female mold section is concentrated by this shape edge at a location radially outward of the center of this surface. In most cases this application of force will sufficiently deform the mold section so that the entire lens will release from the mold. If the lens continues to adhere to the mold a second force applied by the flat face of an axial plunger to the center of the non-optical surface will result in the release of the lens.
However, in the case of a silicone hydrogel lens, this has been found not to be the case in that the application of forces as noted above will not cause the lens to release form the mold. The problem presented by a silicone hydrogel lens is that it is relatively compliant. For example, when fully hydrated, the lens may have a modulus of 70 gm/mm2 or less. While the cured lens still attached to the female mold section is not hydrated, even in its dry state the cured lens still is so compliant that the lens lacks sufficient rigidity to peel or release from the mold as the shape of the mold is distorted first by the flat face of the annular plunger and then by the axial plunger. Instead the silicone hydrogel lens contorts so as to conform along with the mold surface and remains adhered to the optical surface of the mold section even after the mold is distorted.
Accordingly, an object of the present invention is to provide an improved method and apparatus for releasing a compliant ophthalmic article from a concave mold surface.
Another object of the present invention to provide a method and apparatus for releasing a mold compliant ophthalmic article such as a dry silicone hydrogel lens or the like from a concave optical mold surface.
A further object is to effect the release of a mold compliant ophthalmic article such as a silicone hydrogel contact lens or the like from a concave mold surface by causing a continuous peeling separation of the article from the mold surface. An additional object includes releasing a non-hydrated molded ophthalmic lens from a mold by peeling the lens from the mold from a radially spaced location to a central or axial location.
Yet another object is to effect the peeling separation of a compliant silicone hydrogel contact lens from a concave mold surface wherein the peeling starts at the outer edge of the lens and progresses radially towards the lens center.